This invention is in the field of large gears; and more particularly, it relates to an improved method, and apparatus or machine for the fabrication of gears.
Various methods have been used for the fabrication of large gears, from about two feet in diameter on up to 20 feet and larger, depending upon the precision requirements in the gear, its size, physical characteristics required in the material, and the advance of technology.
To avoid the tremendous amount of work, material consumption and energy required in "whittling" or machining a large integral gear out of a single piece of metal, because of high costs, or actual limitations of the available facilities, techniques, machine tools and the like, one early approach was to cast the gear in half or smaller sectors to approximate form. The sectors are then bolted or otherwise secured together, and the cast elements, usually as assembled, thereafter being machined with the required accuracy in the shaft or hub bore, and in the teeth, which can be partially formed by casting in a rim flange structure of the casting or cast assembly.
The various parts of the machined gear element thus produced might be subjected to appropriate metal or heat treating and the like to develop requisite or desired properties at various parts of the structure.
The gears or components can be cast of appropriately formulated special cast iron, or cast steel or steel alloys or of other metals.
At the present time certain gears even in quite large sizes, for some special applications or environments of gear use, the fabrication technique is first to produce a cast gear blank of appropriate size, shape and form approaching as near as possible the ultimately desired gear product shape and dimensions, and thereafter accurately to machine the blank with teeth, and other parts of the gear as now possible with modern machine tooling and facilities.
However, for many years and to the present, the fabrication technique has generally involved the production of a gear blank as a weldment comprised of a web disk plate and a formed ring element fitted or forced onto and welded to the web disk periphery, with certain oversizes in various dimensions; the gear blank is then appropriately machined for face, edge and other dimensions and finally subjected to appropriate machine operations to provide the rim flange with accurately cut teeth of desired size and form.
Usually thereafter the web disk plate is appropriately centrally apertured to receive a solid or hollow cylindrical hub piece which is welded in place. The hub is then machined with a shaft bore and to appropriate axial dimensioning; or an already present central hole can be reamed or bored as a shaft receiving bore coaxial with the pitch circle of the already formed teeth.
However, though apparently less preferred in modern technology, it is possible though usually less convenient, for the hub stock material be incorporated into the weldment before the production of the teeth and other machining.
The present invention is more particularly concerned with an improved method, and apparatus or machine for carrying out the method, for fabrication of gears by production of a weldment gear blank form involving at least a circular web disk plate and a rim flange formed to a closed annular form about and weld-secured on the periphery of the web disk plate.
In the prior art, weldment type gear blanks have been made by first producing a circular web disk plate and a separate ring-formed rim element, the latter produced from straight strip stock of requisite length performed to annular form with rim free ends then being secured or welded together to close the ring. The ring placed about the web disk and secured to the web disk periphery by a welding bead peripherally layed continuously circumferentially between ring and web on both sides of the web.
Ross U.S. Pat. No. 1,908,187 of 1933 uses this method; and then also welds a hollow hub element into place at the central aperture of the disk to provide the complete gear blank weldment; with special concern about using diverse steels in the three components for obtaining different properties in the corresponding regions of the final gear.
Such procedure requires the setting up of equipment for forming the ring and thereafter jigging or setting up a circular web disk plate with the preformed welded ring element properly located thereabout for the operation of welding ring to web.
Where there are slight irregularities on the web disk plate periphery, as indeed there may be even with modern precision torch cutting equipment with which such a web disk may be cut from rolled plate stock, there may be some awkwardness in time consuming operations in bringing the preformed ring into appropriate position. This is especially true in such cases where the preformed ring has been welded closed at its ends. On the other hand, where the ring is not welded closed, it usually requires more complicated jigging. Similar difficulties may arise from out-of-roundness of the ring thus preformed.
By this method approach it can be seen that there is the disadvantage of setting up work in the first instance say for the ring forming from strip stock, and then the welding of the ends thereof, followed by a second set up operation and jigging to bring the ring and the web disk into proper relationship for the circumferential welding as required.